Bridging the "middle ground" between medium range weather forecasting and climate prediction: verifying the accuracy of 14 day outlooks

In 1999, the present author conducted an experiment to establish the limits of predictive capability for the southeast Australian city of Melbourne (Aust. Meteor. Mag., 48:159-167). The results of the experiment, which involved verifying a set of quantitative forecasts for Melbourne out to 14 days, were presented. The data indicated that, even in 1999, it might have been possible to make useful statements about the expected average weather conditions over the 10-day period between days 5 and 14. In a subsequent (2005) paper (Aust. Meteor. Mag., 54:203-211), the present author presented the results of a repeat of the earlier experiment, noting that the work of Lorenz suggested that there is a 15-day limit to day-to-day predictability of the atmosphere. The 2005 paper reported that the results obtained therein suggested emerging evidence that there may now be some day-to-day forecast skill out to Lorenz's 15-day limit, particularly for temperature. A "real-time" trial of a methodology utilised to generate Day-1 to Day-7 forecasts, by mechanically integrating (that is, combining) judgmental (human) and automated predictions, has been ongoing since 20 August 2005 (BAMS, June 2007, 88:850-851). In August 2006, the forecast period was extended to Day 10, by combining climatology and automated predictions. The encouraging performance of the Day-8 to Day-10 component was reported last year in a paper by the present author asking the question, "Does society benefit from very long range day-to-day weather forecasts?" (Symposium on Linkages among Societal Benefits, Prediction Systems and Process Studies for 1-14-day Weather Forecasts, New Orleans, Louisiana, USA 23 Jan., 2008). In January 2009, the forecast period was extended to Day 14. The purpose of the present paper is to report on the system's performance, comparing the results with those achieved earlier.